1. Field of the Invention
This invention relates to orthopedic devices such as casts, splints, and the like; to materials and methods for making same; and to methods of producing certain of the materials which are used in their fabrication. The orthopedic casts, splints and the like are useful in the treatment of the animal or human body for the maintenance of immobilization and fixation following reduction of fractures and disclocations, the maintenance of approximation of bone fragments following reduction of fractures, the maintenance of immobilization and fixation to promote healing in instances of compound fractures and bone disease, the immobilization of inflamed or injured joints in disease or trauma, and the support and immobilization of ligamentous and muscular structures in instances of sprains and strains. The orthopedic devices provided by this invention may also be used as an occlusive dressing for wounds of the extremities by encasing the limb or part to reduce motion and accelerate healing; as a support splint in paralysis or weakness of muscles; and as a means to maintain correction of deformities, either congenital or acquired. They may also be used as a means of protecting or supporting limbs or other body parts during athletic activities and the like.
As used herein the term "orthopedic device" is intended to include devices externally applied to a portion of the human or animal body for any of the above purposes, regardless of whether they may be otherwise categorized as casts, splints, supports, braces, shields, body casts, etc. Specifically excluded from its meaning are devices intended to be surgically implanted in the body, such as bone implants.
2. Description of the Prior Art
Plaster of Paris has long been widely used as a material for fabricating orthopedic casts. Unfortunately, costs made of this material are heavy, bulky, sensitive to water, brittle and relatively easily broken, so that casing may have to be repeated. Moreover, they are difficult to clean and are not soil-resistant, they lack transparency, and have relatively poor x-ray penetrability. They are not very permeable to moisture and thereby tend to trap perspiration, creating a medium for the buildup of bacteria and offensive odors.
In attempting to overcome the problems associated with plaster casts, a number of plastic materials have been employed in orthopedic devices. For example, in U.S. Pat. No. 2,616,418 specific crystalline non-polymeric organic compounds having sharp melting points between 45.degree. C. and 100.degree. C. are admixed with specific high molecular weight thermoplastic substances, such as cellulose acetate, to form cast-forming compositions. U.S. Pat. No. 2,385,879 discloses a plastic cast material comprising a particular plasticizer and a conjoint polymer of a vinyl ester of an aliphatic acid and a vinyl halide.
U.S. Pat. No. 3,420,231 discloses a thermoplastic cast forming material that is flexible and moldable at about 165.degree. F. The sheet contains a fibrous substrate coated with a cast forming material comprising a specific elastomeric type resin, such as trans 1,4-chloroprene polymer and a specific inversely soluble resin, such as methyl cellulose or polyvinyl methyl ether.
U.S. Pat. No. 3,692,023 describes orthopedic casts, splints, and the like which are produced from supported or unsupported webs or sheets of cyclic ester polymers, such as poly-epsilon-caprolactone. Orthopedic casts made from this material display excellent properties and have solved a number of problems exhibited by the various other plastic casts of the prior art. These casts are rigid, non-irritating, strong, durable, water-resistant, and soil-resistant. Further, they are easily removed and can be sterilized and reused. There is no danger of skin irritation due to components, such as plasticizers, separating from the polymer and exuding out of the cast.
Yet, despite the ingenuity displayed in the prior art and the advances which have been made, there are still unsolved problems in the field of orthopedic devices, and particularly in the area of plastic orthopedic devices. Plastic materials generally must be heated above their softening points in order to be applied to the body portion being treated. Some plastic materials, such as the cyclic ester polymers employed in U.S. Pat. No. 3,692,023, are characterized by well defined melting points, above which the melt index rises sharply. In applying such materials as orthopedic casts, they tend to be more fluid at the application temperature than would be desired by the practitioner and, thus, somewhat difficult to handle. Other polymeric materials which have been employed in orthopedic devices have softening or melting points at temperatures which are too high to be comfortably applied to the patient. Ideally, a polymeric material to be used in orthopedic devices should be one which becomes soft and malleable, but not highly fluid, at a temperature which is above room temperature, yet not so high as to cause the patient discomfort during application.
In applying orthopedic casts, practitioners of orthopedic medicine generally prefer to use the cast material in the form of a bandage which can be wrapped around the body portion in overlying layers in order to provide a close conforming fit to the body portion. Orthopedic cast forming materials have been produced in the form of rolled bandages comprising a substrate, such as cotton gauze, having a polymeric coating or impregnation thereon. The roll of bandage material is heated, for example by immersing it in a hot water bath, until the temperature of the polymer reaches its softening point, and the cast is applied by wrapping the heated bandage around the limb or other body part as it is drawn off the roll. A number of problems have occurred when attempting to apply casts in this manner using the prior art known plastic cast forming materials. Due to relatively high melt index at the application temperature and/or high degree of self-adhesion of the polymer, it is frequently necessary to insert a release-coated separating sheet between the layers of the rolled bandage to prevent the layers from fusing or sticking together on the roll when the roll is heated. Further, the outer layers of the rolled bandage tend to insulate the inner layers, resulting in uneven heating. Consequently, the outer layers may be too hot for the comfort of the patient or the inner layers may not be sufficiently heated to allow the practitioner sufficient working time to apply the cast. Although hot water is the most widely used medium for heating plastic orthopedic cast forming bandages, the high heat capacity of the water can result in discomfort to the patient at the relatively high temperatures needed to soften many of the known plastic cast forming materials.